1. Field of the Invention
The invention relates to a rear projection display device, and more particularly to a rear projection display device in which a light shield blocks scattered lights.
2. Description of the Prior Art
Referring to FIG. 1, a conventional rear projection display device 10 includes an image generator 11, a small reflector 12, a large reflector 13 and a screen 14. The small reflector 12 is mounted at a front of the image generator 11. The screen 14 is mounted at a front of the display device 10. The large reflector 13 is mounted at a rear of the screen 14 in a reflecting path of the small reflector 12. The image generator 11 provides image beams 111 that are reflected via the small and large mirrors 12, 13 to project onto the screen 14.
An image displaying element 112 such as digital micro-mirror device (DMD), a liquid crystal panel or Liquid Crystal On Silicon (LCOS) panel in the image generator 11 projects image beams including ineffective beams onto the screen 14 to generate images including scattered images that are formed by the ineffective beams. The image beams may include image beams 111A, 111B and 111C. The image beams 111A may not be projected onto the small reflector 12 but the screen 14. The image beams 111B may be projected at a periphery of the small reflector 12, and then reflected onto the screen 14 via the small reflector 12. The ineffective beams 111C may be reflected onto the screen 14 via the small reflector 12 or the large reflector 13.
There are several approaches to overcome the above disadvantages. For example, a light shield 1131 is attached on a lens 113 of the image generator 11 as shown in FIG. 2. Alternatively, a light shield 1121 is attached into the image displaying element 112 to block the image beams from being projected onto ineffective areas of the screen, as shown in FIG. 3. However, the light shields 1121, 1131 tend to block the image beams that are to be projected at effective areas of the screen. The size of the light shield 1121, 1131 cannot be exactly controlled, and the light shield cannot be adjusted, neither. Therefore, adding the light shield cannot effectively avoid the adverse affect of the images at the ineffective areas on the displayed image quality.